Efficacy of Predators Attacking Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) Eggs on Grain Sorghum in the Field

Abstract

Exclusion and insecticidal disruption studies were conducted to evaluate the efficacy of predators of corn earworm, Helicoverpa zea (Boddie), eggs on grain sorghum panicles in southwest and northeast Arkansas. Sets of three grain sorghum plants in a field were selected and one of three different treatments were applied to each plant in the trio. One panicle was fitted with an open cage with a large mesh that allowed colonization by most arthropod predators (particularly Orius insidiosus (Say)), but prevented feral H. zea moths from ovipositing on the panicles. The other two panicles in each trio were sprayed with mevinphos (Phosdrin) to erradicate predators, then one of these panicles was fitted with a cage of fine mesh that excluded all predators (total exclusion). The third panicle was covered with only a large mesh cage (insecticidal disruption). Ten H. zea eggs were placed on each of the panicles and the number that were shriveled or missing (indicative of predation) were recorded after 24 and 48 h. Predator densities also were evaluated on these and adjacent panicles. Tests were replicated in two locations over two years. When predator densities were highest, an average of 8.7 O. insidiosus (all stages) were found per panicle in open cages. Differences in the numbers of eggs shriveled or missing were significant in these treatments, with 62% missing from open cages, 27% from insecticidal checks, and only 15% from total exclusion cages. Because O. insidiosus represented 94% of the total predator population, the results indicated the importance of O. insidiosus as a predator of H. zea eggs on grain sorghum. The insecticidal disruption method appeared to be an effective technique for evaluating the efficacy of predators of H. zea eggs on grain sorghum panicles.